Dial switch with stationary blades having cutback edges



Dec. 8, 1953 w. c. SEALEY 2,662,130

DIAL SWITCH WITH STATIONARY BLADES HAVING CUTBACK EDGES Filed June 30, 1952 Patented Dec. 8, 1953 DIAL SWITCH WITH STATIONARY BLADES HAVING CUTBACK EDGES William C. Sealey, Wauwatosa, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application June 30, 1952, Serial No. 296,366

(Cl. ZOO- 11) 7 Claims.

This invention relates generally to dial switches and more particularly to the contact elements oi such switches.

Dial switches to which this invention relates are embodied in regulating equipment of the stationary induction type in which the windings of a transformer are selectively connected to a load or a line through conventional tap changing equipment which includes the dial switch. An example of a dial switch utilized in such voltage regulating equipment is illustrated in my U. S. Patent 2,399,943 granted May '7, 1946, for an Electrical Regulating Apparatus.

It is an object of this invention to provide a dial switch in which the potential difference between adjacent xed contact blades can be increased thereby increasing the allowable voltage between taps on the windings of the regulator in which the dial Switch is embodied.

Another object of this invention is to reduce the size of dial switches by decreasing the required diameter of the circle on which the fixed contact blades are circumferentially spaced while maintaining the comparative ease of rotation of the movable shoes from one xed blade onto the next iixed blade.

Still another object of this invention is to improve dial switches having two pairs of circumferentially spaced movable shoe contact elements that cooperate selectively either with a single iixed switch blade or with adjacent circumferentially spaced fixed switch blades, by increasing the clearance between the adjacent fixed blades and by reducing the electrical stress at the edges of the fixed blades while maintaining the comparatively long inclined edge surfaces on which the pairs of movable shoe contacts must make rubbing engagement.

And still another object of this invention is to increase the clearance between circumferentially spaced xed blades of a dial switch without reducing the length of the upper and lower contact faces of the blades, without reducing the effectiveness of the tapered contact engaging edge portions of the blades that evenly and uniformly separate the pair of movable shoes as they move onto the blade, and without appreciably flexing the conductive shunts fastened to the movable shoes. y

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with accomJ panying drawingsin which:

Fig. 1 is a plan view of a dial switch embodying this invention;

Fig. 2 is an enlarged partial View of two adjacent fixed blades of the switch shown in Fig. 1;

Fig. 3 is an enlarged plan View of a portion of a iixed blade and one pair of contact shoes of the rotary Contact assembly of the switch of Fig. l, with the shoes shown displaced so as to engage with the tapered edge portion of the blade;

Fig. l is a sectional view taken along line IV--IV of Fig. 3; Y y

Fig. 5 is an enlarged sectional view of part of the switch of Fig. l, with the shoes displaced to show the engagement of the curved contact surfaces of a pair of contact shoes with the tapered contact engaging edge portion of a iixed blade;

Fig. 6 is an enlarged plan view similar to Fig. 3 or a modified embodiment of the dial switch contact elements;

Fig. 7 is a sectional View showing the engagement of the contact surfaces of a pair of movable shoes and a prior art fixed blade that has a length of tapered edge portion of the blade removed for example to increase the circumferential clearance between adjacent blades;

Fig. 8 is a plan View similar to that of Fig. 3 of another embodiment of the dial switch contact elements; and

Fig. 9 is a sectional View taken along line IX--IX of Fig. 8.

The dial switch illustrated in Fig. l includes an insulating panel II on which a plurality of contact blades I2 are xed by suitable fastening means (not shown). These blades are disposed on a circle about the center of the dial switch and are equally spaced circumferentially from each other so that one blade or two adjacent blades may be selectively engaged by a rotary Contact assembly I3 having two pairs of circumferentally spaced contact shoes I4 and I 5.

The contact shoes are identical to each other and the similar, oppositely disposed curved contact surfaces I6, I7 of a pair cooperate with opposite faces IS, I9 of each of the blades. Each of the contact shoes is carried by arm 2| which may be rotated about the center of the switch by shaft 22. It is desirable that considerable conta-ct pressure be exerted on the stationary or xed blades by the shoesso that the switch will carry heavy load currents without excessive heating of the contact elements, and this force applying means is illustrated as springs 23 which are suitably fastened at one end to the rotating arm and have their opposite ends conned between the sides 24, 25 of the trough shaped contact shoes, as can be seen in Fig. 5. Each spring firmly presses on rivets 2, 28 which connect the outer end of a conducting shunt 29 of thin strips of copper to the shoe. The inner end of the shunt is fastened by suitable means (not shown) to one of the brushes 3l, 32 engaging collector rings 351 3A in awell knowninanner.`

As rnentionedabove, the oppositely disposed contactslrfacesof `the shoes are curved; preferably these are segmental cylindroidal portions that are curved in cross section normal to a ral trated have contact with the stationary rblades along a line radial of the centerfoftheswtch.`

The circumferentially spacedendporti'ns d5' of each of the blades are tapered from their opposite upper and lower faces IB, rI 9 .to their median plane so as to present a gradual inclineon whichy the shoes rub as they move onto a blade." The angle betweenthe inclined surfaces or tapered end portions sufficiently 'small' to provide a uniform wedgiingfactiont' force the shoes apart and t'presenta slight incline andminirnum resistance t separation of the shoes.

' VIn"`order"to"reduce the size of the dial switches or to increase the electrical potential 'diiference thatimay be'imposed .between any two adjacent bladsthe "space between the adjacent end portions of contiguous blades isv'i'ncreasedfand in they converge toward each other along radial lines. The incline or taper of the end portions is constant along the entire radial length of both the outermost and innermost parts. As a result the extreme edge of the innermost part is a generally triangularly shaped, blunt surface that eifectsa jArediiction of the electrical stress.

As can be seen from the plan view of Fig. 3

the cut back edge 42 of the innermost part inle tersects with the outermost part at a point 43 dial line from the center of the dial ,.sv v itch.:, Thus, these surfaces of a pair of the shoesillusthat Amay be., more distant radially from the centerfof-I the Ydialswitch than the middle or center of the shoes. Therefore, in order that .hftheV shoes Iopen properly so that the oppositely .disposed surfaces thereof move substantially parallel to each other as the pair of shoes move'onto.astationary blade, the rivets connecting .the shoes to the conductive shunts are disposed radially from the center of the dial switch a distance equal to or beyond the point of inters'ecticjin of theA edges of the outermostand "innermost parts of the blades. Thus, the force of the springs 4is exerted on the shoes radially beyondthebut back thereby providing means in tle ysfwitch'for keeping the shoes parallel to .eachf'other as theyY move onto the stationary )'blade.' "This prevents the shoes from pivoting aboutA the heel" 44 thereof as Vthose .shoes are moved onto the blade fas would otherwise occur accordahcewith'this invention thatJ increase vingr) Abemge' gf the shoes riding up the Cut back curnf'erentialy lengthof the upper and lower `faces of the blades. Eor to diminish that face length `betweentapered end'portions would alfect the operation' of the switch in 'that all four shoes of the rotary assembly must firmly and evenly `press on tlisefac'es of a blade in' alternate switch positions, y and a minimum tolerance'of length of the"- faces'is desired. Furthenthe effectiveness of the ygradual incline of the'end portions of the blades is retained although" the Vclearance 'between' 'adjacent bladesis increased.

It is'"i in'clesi iable"t`o merelycut off the leading edge f'the tapered end""portio'n of the blade as shown iln Fig. 7 because such a' 'prior artarraileementrehIts'iri a relatively blunt abutment ofthe blade 6B with the shoes 6 1, 6 8 with a relatively 'steepv angle "offi'ncline for separating the" shoes as they iove 'ontdthebladel This'wuldneces- Asitate increasing" the 4force required for moving Fthe shoesifrornone'postion t`o` the neat.v

' Inl the illustrated' ``embodiments this increase in clearance betweenadjacentblades while maintaining the full effectiveness of the inclined v'end portionsiisinade possiblefby reshaping a part 'of those"tapered'"eridportions and' by making the springs in the rotary' assembly exert a force Aon 'the shoes at va certainradial distance" from the center"'of" the dial switch. rIhat' is,'th'e forces `of they springs are exerted on the shoes iat' particular locations'with respect to the tapered end portions of the' stationary blades; The shapeand arrangement ofthe Ico'n'ta'ztelements to" effect this irnprovenient inthe dial switch is illustrated best 'in Figs. 3'to 5*.' lThis extreme edge 4I of the ontermostpart of the end portion of each blade preferablyextends radially ofthe center of the dial switcni while the extreme 'edge 42 of the inner- `xnost part'pf `ea`ch end portion is cut back from the outermost edge'on a diagonal Vline as vseen in the planyiew of Fig'i3. The adjacent'cut back parallel'to eachother (Fig. 2) whereas otherwisel bluntedge' of theinhermost part'as shown in Figs. '8 and '9 for a'less desirable embodiment in which thevsprings 5I, 52`ei'iert a force .though rivets 5`3, 5 4` n the'innermost part 55.

' Theifnodificat'ion illustrated in Figff differs from the Vemb@diment vshown in Fig. 3 only in that Ithec'ut bacl'edge '61 of the innermost part of the blade does" not extend radially as far away from the centerY of the dial switch as for the r`i0 structre represented in Fig.` 3. In fact, the

Lvintersect'i'o'rr of the extren'fie edges of the innermost'a'ndcutermostparts' of the blade occurs at apoi'r'it`6`2u apprxi'matelyat the midpoint of the shoes. For A'this'"relatively short cut back,

45 the position`of the rivets 63 may `be at the midpoint of the shoes, Aand the forces exerted by the Springseil pressjapprximateiy at that point of intersection s`th at the line 'contact between the shoes andihclin'e of the blade will bexnainthe ed pticnfo'f 'the blade. f `The"cnt iol'cf the action of the shoesvby the forceA offtheV spring is'very important.' First, sincey it prevents tipping' of V`the"shoffabcu'tfthe 55 Heel 'thereof it redii'cesj the flexing of the conducte 'shiiitg4 thereby" lengthening the Vlifgff those"shi'nts which are hiade preferably from thin `sheets of copper strip.' `Inadditidn,it assuresthatvvhereniefaces of themed@ are nat 6o 'there' will be line" contact between theV sho'esarid if th'slioes -pivot'daboiittheir heel as they rode u'ptrre blunt 'dge'of thejcut backwpai-tf "The peratior'i of "a" dial switch embodying the teaching'b'f this' invention 'remains substantially the same as in switches of the prior art butthe invention makes it possibleto materially decrease the size of thei'switch '01",v asmentioned above,v to `increase the clearance between adjacent fixed contact blades. The angle of incline which the shoes'must rise in Vgoing on to ...the 'stationary :175 blades is relatively smalll and may be as'small as desired so that a minimum of forceis-required to move the rotary contact assembly up the angle of incline and across the blade.

Although but few embodiments of the present invention have been illustrated and described it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

y 1. A dial switch comprising an insulating panel, a plurality of stationary contact blades fixed to said panel and spaced radially about a center point and circumferentially spaced from each other, and a movable contact assembly which is rotatable about said center point, said assembly including two pairs of contact shoes radially spaced from said center point so as to engage with said blades, said pairs of shoes being circumferentially spaced a distance greater than lthe circumferential distance between adjacent portions of said blades and less than the circumferential length of any of said blades whereby said two pairs of shoes may be made selectively to cooperate with the same blade or with adjacent blades, said shoes disposed on opposite sides of the median plane of said blades whereby said shoes rub on opposite faces of said blades, said assembly including means for biasing said shoes toward each other whereby said shoes are firmly pressed on the opposite faces of said blades, the opposed surfaces of said shoes being segmental cylindroidal portions curved in cross section normal to a radial line from said center point, the outermost part of each of the circumferentiaily spaced end portions of each of said blades being tapered to substantially the median plane of the blades and the innermost parts of each of said end portions terminating on a line which makes an obtuse included angle with the extreme edge of the corresponding outermost part, the extreme edges of said innermost parts of adjacent said blades being substantially parallel to each other, and said biasing means exerting a force on said shoes at a distance greater than the radial distance of the point of intersection of said extreme edges of said corresponding innermost and outermost parts.

2. A dial switch comprising an insulating panel, a plurality of stationary contact blades fixed to said panel and equally spaced radially about a center point and circumferentially spaced from each other, and a movable contact assembly which is rotatable about said center point, said assembly including two pairs of contact shoes radially spaced from said center point so as to engage with said blade, said pairs of shoes being circumferentially spaced a distance greater than the circumferential distance between adjacent portions of said blades and less than the circumferential length of any of said blades whereby said two pairs of shoes may be made selectively to operate with the same blade or cooperate with adjacent blades, said shoes disposed on opposite sides of the median plane of said blades whereby said shoes rub on opposite faces of said blades, said assembly including means for biasing said shoes toward each other whereby said shoes are iirmly pressed on the opposite faces of said blades, the opposed surfaces of said shoes being segmental cylindroidal portions curved in cross section normal to a radial line from said center point, the outermost part of each of the circum- 6 ferentialiy spaced end portions of each of said blades being tapered to substantially the median plane of the blade and the innermost part of cach of said end portions terminating on a line which makes an obtuse included angle with the extreme edge of the corresponding outermost part, and said biasing means exerting a force on said shoes at a distance at least as great as the radial distance of the point of intersection of said extreme edgesrof said corresponding innermost and outermost parts.

3. A dial switch comprising an insulating panel, a plurality of stationary contact blades fixed to said panel and spaced radially about a center point and circumierentially spaced from each other, and a movable contact assembly which is rotatable about said center point, said assembly including two pairs of contact shoes radially spaced from said center point so as to engage with said blades, said pairs of shoes being circumferentially spaced a distance greater than the circumferential. distance between adjacent portions of said blades and less than the circumferential length of any of said blades whereby said two pairs of shoes may be made selectively to cooperate with the same blade or with adjacent blades, said shoes disposed on opposite sides of the median plane of said blades whereby said shoes rub on opposite faces of said blades, said assembly including means for biasing said shoes toward each other whereby said shoes are firmly pressed on the opposite faces of said blades, the opposed surfaces of said shoes being segmental cyiindroidal portions curved in cross section normal to a radial line from said center point, each of the circumierentially spaced edge portions of each of said blades being tapered and providing a broken line extreme edge for each of said portions in which the outer part of said broken line is in the median plane oi said blades and extends substantially radially of said center and the inner part of said broken line extends diagonally across the taper of said end portion, said shoes being of radial length suliicient that more than half of the radial length of each of said shoes engages said blades radially beyond the inner end of said outer part, and said means contacting said shoes radially from said center point at least as distant as the inner end of said outer part.

4. A dial switch comprising an insulating panel, a plurality of stationary contact blades fixed to said panel and spaced radially about a, center point and circumferentially spaced from each other, and a movable contact assembly which is rotatable about said center point, said assembly including two pairs of contact shoes radially spaced from said center point so as to engage with said blades, said pairs of shoes being circumferentially spaced a distance greater than the circumferential distance between adjacent portions of said blades and less than the circumferential length of any of said blades whereby said two pairs of shoes may be made selectively to cooperate with the same blade or with adjacent blades, said shoes disposed on opposite sides of the median plane of said blades whereby said shoes rub on opposite faces of said blades, said assembly including means for biasing said shoes of each pair toward each other whereby said shoes are firmly pressed on the opposite faces of said blades, the opposed surfaces of said shoes being segmental cylindroidal portions curved in cross section normal to a radial line from said center point, each of the circumferentially spaced edge portionsnfieach of said' blades being taperediand is rotatable about said center point including a pair of oppositely disposedcontact shoes radially spaced from said center point to selectively engage with said blades, said shoes disposed on opposite sides of the median plane of said blades, said assembly including means for biasing said shoes toward each other whereby said shoes cooperate with the opposite faces of said blades, the outermostpart offeach of the circumferentially spaced end portions of each of said blades being tapered to substantially the median plane of the blade` and the innermost part of each of said end portionsterminating on a line which makes an obtuse included angle with the extreme edge of the corresponding outermost part, the extreme edges of said innermost parts of adjacent said blades being parallel to each other, saidbiasing means exerting a force on said shoes at a dis-- tance greater than the radial distance of the pointofl intersection of said extreme edges of said corresponding innermost and outermost parts.

6. A dial switch having an insulating panel, a plurality of `stationary contact blades xed to said panel and equally spaced radially about a center point and circumferentially spaced from each other, and a movable contact assembly which is rotatable about said lcenter point including a pair of opposltely disposed` contact,` shoes radially spaced from said center point toselectively engage with said blades, said shoes disposed on opposite sides of the median'plane of said blades, said, assembly including means for ,bias- Aing said shoes toward 'eachother wherebysaid shoes cooperate with the opposite facesof said blades, each of the circumferentially spaced edge portions of each of said blades being tapered and providing a broken line extreme edge for each of said portions in which the outer part of said broken line is in the median plane of said blades and extends substantially radially of said center and the inner part of said broken line extends diagonally across the taper of said end portion,

lsaid shoes being of radial length sufficient that more than half of the radial length of` each vof 'said shoes engages said outer part of said blades radially beyond the inner end of said outer part,

, and said means contacting-said shoes onlyl radially from said centerpoint at least as distant as the inner end of said outer part.

7. A dial switch having an insulating panel, a plurality of stationary contact blades fixedto said panel` and equally spaced radially about la center point and circumferentially spaced from each other, and a `movable contact assembly which is rotatable about said center point including a pair of oppositely disposed contact shoes radially spaced from said center point to selectively engage with said blades, said shoes disposed on` opposite sides of the median plane of said blades; said assembly including means for biasing said shoes toward each other whereby said shoescooperate with the opposite faces of said blades, each of the circumferentiallyspaced edge portions of each of said blades being tapered and providing a broken line extreme edge for each of said portions in whichV the outerpart of lsaid broken line is in the median plane of said blades and the inner part of said broken line extends diagonally across the taper of` said end portion, and said meanscontacting said shoes radially from said centerppoint approximately as `distant asthe inner end of said outerpart,

WILLIAM C. SEALEY.

References Citedinthe `Ifile 0f thispatent UNITED STATES .PATENTS 

